If the aircraft is “wet”, that means it has fuel in it. If a student or a renter is going to take one of our aircraft, it comes with fuel. If they go away to another airport, we will reimburse them at our cost. We won't reimburse them if they purchase fuel at a higher price at a different airport.
Some schools don't do it that way. Some operators actually do because the price of aviation fuel floats week to week, as the price of fuel does at the gas pumps. They rent it to the person dry, and for every flight, they figure out how much fuel has been used and apply the cost of the fuel onto the price of the flight.